The present invention relates to an apparatus for controlling the temperature in an enclosure such as a passenger compartment of an automotive vehicle.
Such a system typically comprises a heater and a cooler disposed in an air duct which opens into a vehicle passenger compartment. The heater and cooler are automatically controlled to maintain the temperature in the compartment at a desired set or command value. An air mix door or damper is provided to control the proportion of air flow through the heater and cooler.
Under low cooling load conditions, a compressor or an evaporator of the cooler are maintained on or the compressor is operated in on ON-OFF mode by a defroster switch having a constant changeover temperature level to maintain the temperature of air passing through the evaporator at a constant level. The air mix door mixes heated air from the heater with cooled air from the cooler to provide the desired compartment temperature.
It is not efficient to mix heated air with cooled air due to the irrational waste of power caused by the heater and cooler working against each other. The conventional prior art arrangement further wastes power since the compressor is operated more than necessary. The power wasted by the temperature control apparatus is produced by the engine, resulting in reduced vehicle performance and increased consumption of expensive fuel.
One expedient to solve the problem mentioned above has been proposed, for example, in copending U.S. Patent Application Ser. No. 178,647, filed Aug. 15, 1980 which is assigned to the same assignee as the present application and in which the outlet temperature of a cooler is controlled within predetermined limits in accordance with the difference between a desired set temperature in a passenger compartment and the actual temperature therein in such a manner as to minimize the time the cooler is energized. Minor temperature variations in the compartment occurring while the cooler is off are compensated for by positioning an air mix door.
In more detail, the proposed temperature control apparatus disclosed in the copending prior application comprises a set unit for setting a desired or command compartment temperature for the compartment, a compartment temperature sensor for sensing an actual compartment temperature in the compartment, a temperature control unit including an evaporator and a heater core for discharging temperature controlled air into the compartment, and an outlet temperature sensor for sensing an outlet temperature of the temperature control unit. There is further provided with an operation control unit which functions to turn the outlet temperature control unit on and off. The operation control unit computes a control on temperature and a control off temperature as predetermined functions of the command compartment temperature and the actual compartment temperature, turn the temperature control unit on when the outlet temperature is higher than the control on temperature and turn the temperature control unit off when the outlet temperature is lower than the control off temperature.
Indeed, such a temperature control apparatus may succeed in saving power due to the substantial cut-down in the operation rate of the compressor. However, it still fails to avoid a drawback that the cooling extent tends to become excessive despite a small number of vehicle passengers or short despite a large number of vehicle passengers, making the passengers feel uneasy and detrimenting the power saving efficiency.
Generally, in a passenger compartment of an automotive vehicle, the front seat is positioned substantially at the center and the rear seat at the rear end. In this respect, whereas the upper outlet of air flow duct open into the passenger compartment at the instrument panel is used to blow out air toward the upper half of the body of an occupant on the front seat and therefrom toward an occupant on the rear seat, the lower outlet adjacent to the legs of the front seat occupant is used to blow air concentrically toward the legs of the front seat occupant and the neighborhood. It is thus possible to control the distribution of air to the upper and lower outlets such that, when only the front seat is occupied, the amount of air coming out of the lower outlet is increased relative to that of air blown out from the upper outlet to thereby direct the air principally to the front seat occupant. Also, it is possible to reduce the cooling ability of the compressor by reducing its operation rate without affecting the comfortableness inside the passenger compartment to any noticeable degree. The present invention has been elaborated with these facts in view.